Body fluid homeostasis is critically important for normal physiological function of the cardiovascular system. Recent evidence suggests that t he diagonal band of Broca (DBB) participates in the central regulation of body fluid balance. More specifically, the DBB relays information from high pressure baroreceptors to vasopressin releasing neurons in the supraoptic nucleus of the hypothalamus (SON) and influences drinking behavior. However, it has not been determined how information from peripheral baroreceptors reaches the DBB and how this input modifies the activity of the DBB neurons. The aim of the experiments in this proposal is to determine the role of the DBB and other neural systems in the baroreceptors control of vasopressin release from the SON. This aim will be addressed by conducting in vivo electrophysiological experiments which will examine 1) the effects of peripheral baroreceptor afferent stimulation on magnocellular supraoptic neurons, 2) the role of noradrenergic receptors within the DBB in the baroreceptor-mediated inhibition of vasopressin SON neurons, 3) the source and influence of the noradrenergic innervation of the DBB. This work will provide new information about the organization of the pathways within the central nervous system that mediate the baroreceptor regulation of body fluid homeostasis. This information may provide a model of how baroreceptor afferents regulate neuroendocrine, autonomic and behavioral systems and how this regulation is altered by the development of disease states.